JP6704864B2 - Power converter - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention uses a power converter configured by using a power device capable of controlling conduction/non-conduction, and particularly uses a plurality of circuit units configured by using a power device called a cell, so that it is close to a sine wave. The present invention relates to a power conversion device generally referred to as MMC (Modular Multi-level Converter) capable of outputting a voltage waveform.

In a power system, a power conversion device using power electronics technology is a PCS (Power Conditioning System) for connecting a photovoltaic power generation system, a wind power generation system, and a power storage system to a power system in addition to direct current transmission and a reactive power control device. The application to the etc. is expanding.

In particular, in order to configure a large DC power transmission system or PCS as a highly efficient converter, it is better to increase the DC voltage. One of the voltage type self-excited converters to which the technique of increasing the DC voltage (or arm voltage) is applied is the MMC converter.

FIG. 1 shows a first form example of the MMC type conversion device. The MMC type conversion device 110 according to the first embodiment is arranged between the conversion transformer 100 on the AC system side and the bus lines 103, 104 on the DC side, and connects a plurality of cells 102 which are power devices in series. Then, the main circuit arm 105 of the conversion device is configured and is formed by connecting the Graet's wire by a plurality of arms.

Further, as an internal configuration of the cell 102, a configuration as shown in FIGS. 2 and 3 is typical. The configuration of FIG. 2 is called a half bridge, and the configuration of FIG. 3 is called a full bridge. In either case, for example, an IGBT and one capacitor 204 are provided as a plurality of switching elements having parallel diodes.

In the case of the half bridge configuration of FIG. 2, two IGBTs (200, 201) are connected in series, and capacitors 204 are connected to both ends of the series circuit. Further, the plurality of cells 102 are connected in series by using the connection point 210 of the series circuit and the one end 211 of the series circuit as an external connection terminal. The two IGBTs (200, 201) compare the modulated wave and the carrier wave for PWM control. When the modulated wave is large, the upper IGBT 200 is turned on and the lower IGBT 201 is turned off. When the modulated wave is small, the upper IGBT 200 is turned on. Opening/closing control is performed so that the IGBT 200 is turned off and the lower IGBT 201 is turned on. As a result, when the modulated wave is large, a circuit passing through the capacitor 204 is configured, and when the modulated wave is small, a circuit not passing through the capacitor 204 is configured.

In the case of the full bridge configuration of FIG. 3, in addition to the series circuit of the IGBTs (200, 201), the series circuit of the same configuration is formed of the IGBTs (220, 221). 222 and 223 are parallel diodes of the IGBTs (220 and 221). In this case, the plurality of cells 102 are connected in series by using the connection points 210 and 211 of the two sets of series circuits as external connection terminals. In the case of the full bridge configuration, the modulated wave and the carrier wave are compared for PWM control. When the modulated wave is large, the IGBTs 200 and 221 are turned on and the IGBTs 201 and 220 are turned off, and when the modulated wave is small, the IGBT200221 is turned off. Then, the opening/closing control is performed so as to turn on the IGBT 201220. As a result, a circuit that passes through the capacitor 204 is configured regardless of whether the modulated wave is large or small, but the current flow direction is different.

The half-bridge cell of FIG. 2 can output only a voltage in which the terminal 211 has a low potential and the terminal 210 has a high potential. On the other hand, in the full bridge cell of FIG. 3, in addition to the voltage at which the terminal 211 has a low potential and the terminal 210 has a high potential, a reverse voltage in which the terminal 210 has a low potential and the terminal 211 has a high potential is generated. You can However, in the case of a system composed of the same number of cells, using a full bridge cell doubles the number of devices used. As shown in FIGS. 4 and 5, some cells have a configuration in which a plurality of power devices are connected in series in advance in the cells.

There are several types of main circuit configurations of MMC type converters. FIG. 1 shows a main circuit configuration including a conversion transformer 100, an arm 105 composed of upper and lower cells, and an upper and lower arm reactor 101. The reactor 101 in the arm 105 is necessary to control the current circulating between the arms.

FIG. 4 is a diagram showing a second form example of the MMC type conversion device. In the configuration of FIG. 4, the conversion transformer is changed to the three-winding transformer 100a, and the transformer reacts with the leakage reactance to perform the same function as the arm reactor 101.

FIG. 5 is a diagram showing a third example of the MMC type conversion apparatus. In the embodiment shown in FIG. 5, the transformer for conversion is a staggered transformer 100b, and a DC voltage is produced between the neutral point 104 and the bus 103 via the arm 105. Although the zigzag connection transformer 100b is used, the configuration can be made extremely simple as compared with the configurations of FIG. 1 and FIG.

FIG. 6 is a diagram showing a fourth form example of the MMC type conversion device. In the form of FIG. 5, the arm 105 and the arm reactor 101 are configured in a Δ connection form. In this configuration, the arm 105 must always output both positive and negative voltages, so the bridge must necessarily apply the full bridge shown in FIG. This configuration is used to configure an MMC type reactive power compensator (STATCOM).

The MMC converter is described in detail in Non-Patent Document 1 and Non-Patent Document 2.

Denki Theory B, Vol. 128, No. 7, 2008 "PWM Control Method and Operation Verification of Modular Multilevel Converter (MMC)" Makoto Hagiwara, et al. Denki Theory B, Vol. 132, No. 6, 2012 "Power Flow Analysis and Control of DC Capacitor Voltage for MMCC-DSCC Modular Multilevel Converter" Hideaki Fujita et al.

In the MMC type conversion device (here, for convenience, description will be made with the configuration of FIG. 5), it is inevitable that the voltage value of each cell 102 deviates from its average value. Because, in order to perform the PWM control, the modulated wave is compared with the carrier wave, and when the modulated wave is large, the upper IGBT of each cell 102 is turned on, and vice versa, the lower IGBT is turned off. This is because some ON times are long and some ON times are short.

FIG. 9A shows a state in which a sinusoidal modulated wave S and a triangular carrier C are compared. For example, nine cells 102 are connected in series to form a 9-cell three-pulse system. Each cell compares the sinusoidal modulated wave S serving as a reference with the triangular carrier C (eg, C5) assigned to the self cell, and determines the ON/OFF time of the upper and lower IGBTs according to the size relationship. However, it is clear that there are cases where the ON time of the upper IGBT is long and short for a certain time. As a result, the voltage value of each cell 102 deviates from its average value.

In the conventional MMC type conversion device, the balance of the cell capacitor voltage thus collapsed is determined by the phase of the current flowing through the cell (having information on the direction in which the current flows) and the average voltage of the cell capacitor voltage. This is realized by adding a correction signal to the modulated wave of each phase so that either the upper device or the lower device of the cell is turned on for a little longer depending on the combination of excess and deficiency.

With this method, however, there is no problem in the case of a "clean" voltage or current in which the voltage or current of the power system to which the converter is connected is a "clean" voltage that contains only the commercial frequency component. In the state of "messy" voltage and current that contains many May collapse.

From the above, it is an object of the present invention to provide a power conversion device capable of suppressing cell capacitor voltage imbalance.

In order to solve the above-mentioned problem, in the present invention, "a plurality of cells each composed of a plurality of switching elements and capacitors are connected in series to form an arm and a switching element of each cell is assigned to the cell. A power conversion device that is on/off controlled by comparing the magnitude of a carrier wave and a modulation wave commonly given to an arm,
A power conversion device, wherein the order of carrier waves assigned to the plurality of cells is changed every predetermined period of a modulated wave. ".

Note that the above-mentioned "changing the order of carriers assigned to a plurality of cells" is hereinafter referred to as "carrier rotation".

By including the above means, it is possible to suppress the cell capacitor voltage imbalance that occurs in principle. This is because, by performing carrier rotation, the carrier for deciding one's own ON is changed one by one from the viewpoint of a certain IGBT, and thus the cell capacitor voltage is less likely to be unbalanced.

The figure which shows the 1st example of a form of an MMC type converter. The figure which shows the half bridge form which is one of the cell structures. The figure which shows the full bridge form which is one of the cell structures. The figure which shows the 2nd example of a form of an MMC type converter. The figure which shows the 3rd example of a form of an MMC type converter. The figure which shows the 4th example of a form of an MMC type converter. The figure which shows the structural example of the power converter device which concerns on Example 1 of this invention. The figure which shows the structural example of the power converter device which concerns on Example 2 of this invention. The figure which shows the relationship between the carrier wave and the modulating wave in the first cycle of carrier rotation. The figure which shows the relationship of the carrier wave and the modulation|alteration wave in the next period of a carrier rotation. The figure which shows the relationship between the carrier wave and the modulation wave in the last cycle of carrier rotation. The figure which shows the relationship of the carrier wave and a modulation wave in the first period when performing carrier rotation for every group. The figure which shows the relationship of the carrier wave in the next period at the time of performing a carrier rotation for every group, and a modulation wave.

Examples of the present invention will be described in detail below.

A configuration example of the power conversion device according to the first embodiment of the present invention will be described with reference to FIG. 7.

In the upper part of FIG. 7, the main circuit configuration of the power conversion device illustrated in FIG. 5 is shown. The arms 105a, 105b, 105c of the respective phases are composed of a plurality of cells 102 connected in series. The a-phase arm 105a is configured by connecting n cells 102 of 102a1, 102a2,..., 102an in series from the upper side. Further, a gate pulse generator GPG (GPGa1, GPGa2,... GPAn) is provided for each cell 102 (102a1, 102a2,... 102an), and a gate optical signal 307a (provided by a gate pulse control device 30 described later is provided. 307a1, 307a2,... 307an), the switching elements in the cells 102a (102a1, 102a2,... 102an) illustrated in FIGS. 2 and 3 are ignited. Note that the a-phase arm 105a will be described here, and the arms 105b and 105c of the other phases have the same configuration as the a-phase arm 105a, and therefore the description thereof will be omitted.

The lower part of FIG. 7 shows a configuration example of the gate pulse control device 30 of the power conversion device. The gate pulse control device 30 includes a modulated wave generator 302, a carrier wave phase calculator 303, a gate pulse calculator 308, an optical signal converter 309, and the like.

Among them, in the modulated wave generator 302, some command values 301 are generated as a result of various control calculations such as speed control, voltage control, current control in a higher-order calculation unit (not shown), and the modulated wave generator 302 is generated. It is input to 302. The modulated wave generator 302 calculates the control command value 301 and outputs a three-phase modulated wave S (Sa, Sb, Sc). Since the main circuit configuration of the power conversion device illustrated in FIG. 5 is formed by the three-phase arms 105a, 105b, 105c, three-phase modulated waves Sa, Sb, Sc for each phase are generated.

9a illustrates the a-phase modulated wave Sa, the modulated wave Sa is, for example, a sine wave, and the other-phase modulated waves Sb and Sc are 120 degrees with respect to the a-phase modulated wave Sa, respectively. The sine wave has a phase difference of 240 degrees, but is not shown in FIG. 9a.

The carrier wave phase calculator 303 inputs the timing signal S1 given by the modulated wave generator 302, and outputs carrier waves Ca (Ca1, Ca2... Can) as many as the number of cells. At this time, since it is desired to cross the carrier wave at the zero point of the modulated wave, the modulated wave signal is received from the modulated wave generator 302 as the timing signal S1. Note that, in FIG. 7, for convenience of illustration, the carrier phase calculator 303 only shows in detail the part that outputs the carrier Ca (Ca1, Ca2... Can) of the a phase, but the carrier phase calculator 303 is shown. Also generates carrier waves Cb (Cb1, Cb2... Cbn) and Cc (Cc1, Cc2... Ccn) of b phase and C phase.

FIG. 9a illustrates a carrier wave Ca (Ca1, Ca2... Can) of the a phase. The carrier wave Ca is a triangular wave whose magnitude changes between 1 and 0 (Fig. 9a) or between 1 and -1, and generates a level 0 triangular wave Ca1 for the cell 102a1 when the timing signal S1 is input, for example. Start. The triangular wave Ca1 is a signal having a triple cycle that produces three triangular waves in a period of one cycle of the modulated wave Sa that is a sine wave. The triangular wave Ca2 for the cell 102a2 is also a signal having the same cycle as the triangular wave Ca1, but is started to be generated as a level 0 triangular wave from the point where the phase corresponding to Δt time is shifted with respect to the triangular wave Ca1. Thereafter, similarly, the triangular wave is started to be generated at the same phase delay interval, and the triangular wave Can for the cell 102an is generated as a triangular wave of level 0 from the point where the phase corresponding to the time (n-1)Δt is shifted with respect to the triangular wave Ca1. .. In FIG. 9a, a series of carrier waves Ca (Ca1, Ca2... Can) for the a phase is illustrated as n=9.

The modulated waves Sa, Sb, Sc output from the modulated wave generator 302 and the carriers Ca, Cb, Cc provided by the carrier phase calculator 303 are input to the gate pulse calculator 308, and gate timing signals 306a, 306b, 306c. To get Although FIG. 7 shows the gate timing signal 306a in detail for 3061, 3062,..., 306n, 306b, 306c are similarly configured. Note that the gate timing signal 306a (306a1, 306a2,... Then, the timing is determined so that the lower IGBT 201 is turned off, and when the modulated wave Sa is small, the upper IGBT 200 is turned off and the lower IGBT 201 is turned on. This relationship is similarly applied to other cells. For example, for the cell 102a2, the timing of the IGBT is determined by comparing the modulated wave Sa and the carrier wave Ca2, and for the cell 102an, the timing of the IGBT is determined by comparing the modulated wave Sa and the carrier wave Can.

The optical signal converter 309 outputs a gate optical signal 307 (307a, 307b, 307c) for each cell. The gate optical signal 307 is passed to a gate pulse generator (GPG) for each cell to generate a gate signal for the upper IGBT and the lower IGBT of each cell to operate the converter.

In the present invention, in the gate pulse control device 30 of the power conversion device configured as described above, the carrier phase for each cell is changed at regular intervals. Note that, as described above, changing the carrier phase for each cell at regular intervals is called carrier rotation.

Carrier rotation will be described with reference to FIGS. 9a, 9b, and 9c. Regarding FIG. 9a, as described above, a situation will be described in which the timing signal S1 provided by the modulated wave generator 302 is input and the same number of carrier waves Ca (Ca1, Ca2... Ca9) as the number of cells is output. However, the reference carrier wave in this case is, for example, Ca1. When the timing signal S1 is input, the generation of the level 0 triangular wave Ca1 for the cell 102a1 is started, and for the subsequent n-1 cells 102a2... 102a9, the phase corresponding to the time of Δt is sequentially delayed to obtain the level 0 level. Generation of triangular waves Ca2... Ca9 has started. The generation start order in this case is Ca1→Ca2→Ca3→Ca4→Ca5→Ca6→Ca7→Ca8→Ca9.

On the other hand, in the carrier rotation, the order of the carrier waves Ca is changed as shown in FIG. In this case, the reference carrier wave is, for example, Ca9. When the timing signal S1 is input, the generation of the level 0 triangular wave Ca9 for the cell 102a9 is started, and the subsequent n-1 cells 102a1... Generation of triangular waves Ca1... Ca8 has started. The generation start order in this case is Ca9→Ca1→Ca2→Ca3→Ca4→Ca5→Ca6→Ca7→Ca8.

The reference carrier wave is sequentially changed after a lapse of a certain number of cycles, and FIG. 9c shows a state in which the reference carrier wave is finally Ca2, for example. At this time, when the timing signal S1 is input, the generation of the level 0 triangular wave Ca2 of the cell 102a2 is started, and the subsequent n−1 cells 102a1, 102a3,... And the generation of level 0 triangular waves Ca1, Ca3,... Ca9 is started. The generation start order in this case is Ca2→Ca3→Ca4→Ca5→Ca6→Ca7→Ca8→Ca9→Ca1. It should be noted that in the state after the elapse of the next fixed number of turns, the process returns to FIG.

In the case of the first embodiment, which is an example in which the timing signal S1 is generated every cycle, which is composed of 9 cells, the initial state is returned at the 10th cycle. In the above example, the cells that are first fired within these 9 cycles are shown as cells that are sequentially adjacent, but the cells that are first fired next time do not have to be in an adjacency relationship. You just have to stand at the beginning position somewhere within the 9 cycles. Further, this sequential changing process is similarly executed in the other arms as long as it stands at the head position somewhere within the 9 cycles.

By executing the carrier rotation described above, the cell capacitor voltage can be balanced even in a system in which the voltage waveform is “messy”. Especially, the effect is remarkable when used together with the conventional cell capacitor voltage balance control,
The configuration of the entire system is not that shown in FIG. 8 but the signal of the gate pulse converter is not the parallel configuration of the optical cable as shown in FIG. 8, but is a serial cable as a serial cable in the converter panel or in the adjacent panel. By having, it is possible to simplify the configuration.

As the MMC type conversion device, the one shown in FIG. 5 is used for the sake of convenience this time, but it can be used in the same manner in FIGS. 1, 4, and 6.

In the carrier rotation of the first embodiment, the carrier phases are shifted one by one, but this does not necessarily have to be shifted one by one.

As shown in FIGS. 10a and 10b, for example, three sets may be formed (need to be a divisor of the number of cells), and the phase may be rotated for every three sets. In FIG. 10a, the triangular waves Ca1, Ca2, and Ca3 are the first set CA1, the triangular waves Ca4, Ca5, and Ca6 are the second set CA2, and the triangular waves Ca7, Ca8, and Ca9 are the third set CA3. Then, in the first cycle, when the timing signal S1 is input, the generation is started with reference to the level 0 triangular waves Ca1, Ca2, Ca3 of the cells 102a1, 102a2, 102a3 corresponding to the first set CA1. The generation start order in this case is Ca1→Ca2→...→Ca9.

In the next cycle, when the timing signal S1 is input as shown in FIG. 10b, generation is started with reference to the level 0 triangular waves Ca7, Ca8, Ca9 of the cells 102a7, 102a8, 102a9 corresponding to the third set CA3. .. In this case, the order of starting generation is Ca7→Ca8→Ca9→Ca1→Ca2→Ca3→Ca4→Ca5→Ca6.

In the next cycle, when the timing signal S1 is input, generation is started with the level 0 triangular waves Ca4, Ca5, Ca6 of the cells 102a4, 102a5, 102a6 corresponding to the second set CA2 as a reference. The generation start order in this case is Ca4→Ca5→Ca6→Ca1→Ca2→Ca3→Ca7→Ca8→Ca9.

The effect of the carrier rotation of the second embodiment is slightly inferior to that of the first embodiment, but there is an advantage that the calculation amount of the control device is small and the load on the control device is light. The other points are the same as in the first embodiment.

30: Gate pulse control device 100, 100a, 100b: Conversion transformer 102: Cell 103, 104: DC side bus 105: Arm 110: MMC type conversion device 200, 201, 220, 221: IGBT
204: Capacitor 210, 211: Terminal 302 Modulated wave generator 303: Carrier wave phase calculator 306: Gate timing signal 307: Gate optical signal 308 Gate pulse calculator 309: Optical signal converter 301: Command value GPG: Gate pulse generator S, Sa, Sb, Sc: Modulated waves Ca, Cb, Cc: Carrier wave

Claims (4)

A plurality of cells configured by connecting a series circuit of switching elements to a capacitor in parallel are connected in series to form an arm, and one end of the arm is an AC connection end connected to one phase of AC, The end is a direct current connection end connected to one pole of direct current, and the switching element of each cell is on/off controlled by comparing the carrier wave assigned to the cell and the modulation wave commonly given to the arms. A power conversion device,
The power is characterized in that the ON times of the two switching elements forming the series circuit are made different, and the order of the carrier waves assigned to the plurality of cells is changed at every predetermined cycle of the modulated wave. Converter. The power conversion device according to claim 1, wherein
The order of carrier waves allocated to the plurality of cells is, when the number of cells is n, the order of the first cell, the second cell... The nth cell in the first cycle of the modulated wave, and In the next predetermined cycle of the modulated wave, the order is the n-th cell, the first cell, the second cell... The (n-1)th cell, and the (n-1)th predetermined cycle of the modulated wave is the n-th cell. −1 cell, nth cell, first cell,... Nth-2th cell in order. The power conversion device according to claim 1, wherein
The order of carriers assigned to the plurality of cells is such that m sets of cells are formed by the plurality of cells, and in the first period of the modulated wave, a first cell set, a second cell set... The order of the m-th cell set, and in the next predetermined cycle of the modulated wave, the m-th cell set, the first cell set,... , The m-1th predetermined cycle of the modulated wave, the m-1th cell set, the mth cell set,... The power conversion device is characterized in that the order of is fixed. The power conversion device according to claim 1, wherein
The order of carrier waves assigned to the plurality of cells is such that, when the number of cells is n, all of the plurality of cells are in the first order in any of the predetermined cycles of n times. Power conversion device.

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